President Barack Obama laughs during a meeting in the Oval Office, Jan. 24, 2011. (Credit: Official White House Photo by Pete Souza)

Pat Buchanan put it bluntly in one of his recent columns: “Consider the most loyal of Democrat constituents in presidential elections: African Americans. They are 13 percent of the electorate but a fourth of the national Democrat vote.” That share may not seem like much, but in a crowded field for the presidential nomination, blacks are can play kingmaker, especially because more than any other group, they vote as a bloc. In general elections, blacks vote Democrat at rates never lower than 80 percent, and sometimes much higher, and during the party’s nomination process, blacks still vote together. In the 2016 race for the nomination, 75.9 percent of blacks voted for Hillary Clinton. The white vote was split almost exactly down the middle: 48.9 percent for Mrs. Clinton and 49.1 percent for Mr. Bernie Sanders.

In 2008, unsurprisingly, Barack Obama beat Hillary Clinton among blacks by eight — and sometimes nine — to one. Vox noted that “Obama won every primary in the eight states where more than 20 percent of the population is black.” This included the very important early state of South Carolina. The nomination fight was very close; Mr. Obama beat Mrs. Clinton by less than half a million out of over 35 million votes. Hispanics supported Mrs. Clinton over Mr. Obama almost two to one.

This means that in 2008, black voters – all by themselves – kept Mrs. Clinton from winning the nomination, and eight years later they guaranteed her victory. To win the Democrat nomination, a candidate has to carry the black vote.

This makes the race hard for political outsiders, or even ordinary politicians who aren’t very well known by blacks. Mayor Pete Buttigieg is an example. He is a young, moderate who was in the military, and has earned plenty of support and attention from important media. But he was almost unheard of on a national level before 2019, and despite campaigning hard for months, blacks do not care for him. Politico put it bluntly in a recent article: “‘On life support’: Buttigieg’s struggles with black voters threaten his candidacy.” Its opening paragraphs explain:

Over the past month and a half, he has invested more money advertising in South Carolina, where a majority of Democrats are African American, than any of the non-billionaire Democrats running for president. . . . But the more than $2 million Buttigieg poured into TV and radio ads, some featuring black supporters touting the former South Bend (Ind.) mayor, hasn’t budged his stubbornly low poll numbers in the state — 2 percent among African American Democrats in a recent Fox News poll.

Last November, Michael Harriot, a black writer at The Root, wrote an article called, “Pete Buttigieg Is a Lying MF” — MF stands for “Mother Fucker.” Mr. Harriot wrote about how hard it is to be black and poor in the United States, and suggested that Mr. Buttigieg knows this, but lies about it. In response, the white presidential candidate called the author on the phone in hopes of mollifying him. Mr. Harriot then wrote a column about the conversation, saying he still couldn’t be sure how honest Mr. Buttigieg was, concluding, “The only thing I actually know about Pete Buttigieg is that he is a white man.”

Two months later, “Mayor Pete” has spent about one million dollars for each percentage-point gain in black support in South Carolina. Ethnomasochism rarely impresses non-whites — especially blacks — but Mr. Buttigieg doesn’t have a choice if he wants the nomination. For whatever reason, blacks do not like Mr. Buttigieg, who desperately needs them; all he can do is grovel and buy ads.

Mr. Sanders, whose consistent democratic socialist principles have inspired millions, faces the same problem. His support among blacks has never been high, and South Carolina polls suggest he has not made much progress. Vice President Joe Biden has a commanding lead, at 36.5 percent, with Mr. Sanders a distant second, at 16.2 percent. Meanwhile, in Iowa Mr. Sanders trails Mr. Biden by just 3.3 percent, and in New Hampshire Mr. Sanders is ahead of Mr. Biden by nearly 5 percent. Needless to say, the population of South Carolina is very different from that of New Hampshire and Iowa.

All the same, Mr. Sanders’s popularity has frightened many within the Democrat Party who think he’s a dangerous radical. But the anti-Sanders wing needn’t worry; there is one thing they can, and very well may, do that will certainly torpedo him: have Barack Obama endorse Joe Biden.

If this happens, whatever support Sen. Sanders has among blacks will evaporate and keep it well below 10 percent. As shown earlier, monolithic black support for Mr. Obama in 2008 won him the nomination, and in the general election, 95 percent voted for him. In 2012, 93 percent of blacks voted for Mr. Obama. Throughout his presidency, black approval always stayed above 80 percent — and was sometimes double that of Americans as a whole. Most blacks will do what Mr. Obama tells them.

By all accounts, Mr. Obama is not a fan of Mr. Sanders, and rumors have been swirling for months that he may step in to ensure that the Vermont Senator does not get the nomination. As CNBC reported in November:

Former President Barack Obama on Friday warned Democratic primary candidates to avoid leaning too far left in their campaigns, and raised concerns that certain liberal policy proposals on health care and immigration might have gone further than public opinion. In an unusual address to a room of wealthy Democratic donors, Obama urged Democratic candidates to be pragmatic in their messages to voters. While he didn’t mention any specific presidential primary candidate or proposal, Obama warned that the average American voter does not align with views from ‘certain left-leaning Twitter feeds or the activist wing of our party.’

So although Mr. Sanders inspires millions of whites to get involved in politics, he has a fatal weakness. If he wins Iowa and New Hampshire, Mr. Obama will almost certainly endorse Mr. Biden, and the Sanders campaign will almost immediately lose any chance of victory.

Mr. Obama’s power will not fade any time soon. He is young for a former President: only 58. Assuming he lives to be 80, he has another 22 years to play kingmaker within the Democrat Party, and there is no countervailing force. Former Presidents Jimmy Carter and Bill Clinton are older, white, and less popular. Flouting the wishes of blacks within the party would require a candidate that brings together most whites and most Hispanics. It’s not impossible, but not likely.

Today, many white progressives are full of hope that Mr. Sanders can fight the media elites and the Davos class within their party and win. But for all their hatred of big business, the military-industrial complex, and special interest groups, what most stands in their way is the fact that blacks, unlike whites, vote as a group. To fix that problem they’ll need more than socialism.